Bovine lentivirus induces early transient B-cell proliferation in experimentally inoculated cattle and appears to be pantropic

Transcriptome Analysis of Bovine Macrophages (BoMac) Cells after Infection with Bovine Immunodeficiency Virus

Introduction

Bovine immunodeficiency virus (BIV) is found worldwide in cattle under natural conditions. However, the effect of BIV infection on immune functions has not been fully characterised.

Material and Methods

Transcriptome analysis of BoMac cells after in vitro infection with BIV was performed using BLOPlus bovine microarrays. Genes identified as differentially expressed were subjected to functional analysis with the Ingenuity Pathway Analysis software (IPA).

Results

Out of 1,743 genes with altered expression, 1,315 were mapped as unique molecules. In total, 718 genes were identified as upregulated and 597 genes as downregulated. Differentially expressed genes were involved in 16 pathways related to immune response. The most enriched canonical pathway was leukocyte extravasation signalling. Interleukin-15 (IL-15) production was indicated as the most activated pathway and the 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 4 (PFKFB4) signalling pathway was the most inhibited one. In addition, the study showed that the inflammatory response was decreased during BIV infection.

Conclusion

This is the first report to describe the microarray analysis of changes in gene expression upon BIV infection of bovine macrophages. Our data indicated how BIV influences the expression of genes and signalling pathways engaged in the immune response.

First evidence of bovine immunodeficiency virus infection in Mexican cattle

This study set out to identify the presence of bovine immunodeficiency virus (BIV) in animals geographically located in Mexico. BIV was first discovered in the United States in a dairy cow with persistent lymphocytosis, lymphoid hyperplasia and lymphocytic encephalitis. Many studies indicate that BIV infection is globally distributed, but its presence in Mexico remains unknown. We collected 1,168 heparinized blood samples from cattle in ten states across the Mexican Republic, then separated plasma using centrifugation and tested for antibodies against BIV. We used an indirect ELISA based on the use of a synthetic peptide derived from transmembrane glycoprotein (gp45/TM). In order to identify the viral genome, we designed a synthetic gene as a PCR control, as well as a pair of oligonucleotides for amplifying a 519 bp product of the env gene which encodes the surface protein. Positive amplicons were purified and subjected to nucleotide sequencing. A total of 189 (28.94%) tested plasma samples suggest the presence of specific anti-BIV antibodies in all states studied except for Chiapas. Additionally, PCR results identified six positive cows in the states of Puebla and Coahuila. BIV in these cows was confirmed via nucleotide sequencing and in silico analysis of these samples. This is the first report of the presence of BIV in Mexican cattle.

Bovine immunodeficiency virus: a lentiviral infection

The bovine immunodeficiency virus (BIV) is a lentivirus which is known to infect cattle worldwide. Though serological and genomic evidence of BIV in cattle has been found throughout the world, isolation of the virus has been reported only from few places. Very little is known about its impact on animal health status, pathogenesis and mode of transmission. BIV is considered generally non-pathogenic and is not known to cause any serious disease in cattle. BIV is genetically and antigenically related to Jembrana disease virus (JDV), the cause of an acute disease in Bali cattle (Bos javanicus) and human immunodeficiency virus, the cause of acquired immunodeficiency syndrome in human. Therefore, it is important to monitor the presence of BIV in cattle to keep vigil over its possible evolution in its natural host to emerge as pathogenic lentivirus like JDV. Differentiation of BIV infection in cattle from the acutely pathogenic JDV is important for diagnosis of the latter. Currently, BIV is considered as a safe model for understanding the complex genome of lentiviruses. Further research on BIV is indeed needed to elucidate its possible role in animal health as well as for insight into the molecular mechanisms adopted by related lentiviruses.

Flow cytometric analysis of lymphocyte subset kinetics in Bali cattle experimentally infected with Jembrana disease virus

Jembrana disease virus (JDV) is an unusual bovine lentivirus that causes an acute and sometimes fatal disease after a short incubation period in Bali cattle (Bos javanicus). The pathological changes occur primarily in lymphoid tissues, which feature proliferating lymphoblastoid-like cells predominantly throughout parafollicular (T-cell) areas, and atrophy of follicles (B-cell) areas. Five Bali cattle were experimentally infected with JDV and all developed typical clinical signs of Jembrana disease characterised by a transient febrile response, enlargement of superficial lymph nodes and a significant leukopenia. Flow cytometric analysis of PBMC during the acute (febrile) disease phase showed that the reduced number of lymphocytes was due to a significant decrease in both the proportion and absolute numbers of CD4(+) T cells, but not CD8(+) T-cells or CD21(+) B-cells. At the end of the febrile phase, total numbers of both CD8(+) T-cells and CD21(+) B-cells increased significantly, while CD4(+) T-cell numbers remained below normal values, resulting in a significantly reduced CD4(+):CD8(+) ratio. We speculate that the persistent depletion of CD4(+) T cells following JDV infection, through lack of CD4(+) T cell help to B cells, may explain the lack of production of JDV-specific antibodies for several weeks after recovery despite an increase in CD21(+) B cell numbers. Further, our previous data showing that IgG(+) plasma cells are targets for JDV infection, correlated with our current data demonstrating an increase in CD8(+) T cell numbers, supports the suggestion that anti-viral cytotoxic T cell or other cell-mediated immune responses may be critical in the recovery process, although this remains to be formally demonstrated for JDV.

Prior bovine immunodeficiency virus infection does not inhibit subsequent superinfection by the acutely pathogenic Jembrana disease virus

In cattle the interaction between the two genetically and antigenically related bovine lentiviruses, the acutely pathogenic Jembrana disease virus (JDV) and the non-pathogenic Bovine immunodeficiency virus (BIV) has not been reported although both JDV and a BIV-like virus have been reported in the Bali cattle (Bos javanicus) population in Indonesia. The outcome of infection of Bali cattle with the R29 strain of BIV prior to superinfection 42 days later with JDV(TAB/87) was determined. All BIV-inoculated cattle were successfully infected and developed an antibody response to the TM and CA proteins. BIV infection did not prevent subsequent infection with JDV or ameliorate the clinical signs of Jembrana disease in the infected cattle. It did, however, modify the dynamics of the JDV infection with an earlier onset and end of the acute disease process, and a reduction in the duration of viremia that exceeded 10(6) genome copies/ml of plasma.

Bovine immunodeficiency virus produces a transient viraemic phase soon after infection in Bos javanicus

Infection of Bali cattle (Bos javanicus) in Indonesia with a non-pathogenic bovine lentivirus similar to Bovine immunodeficiency virus (BIV) is suspected but efforts to detect the virus have been unsuccessful. To define the kinetics of BIV infection in Bali cattle, 13 were infected with the R-29 strain of BIV and monitored for 60 days. No clinical effects were detected. Proviral DNA was detected in peripheral blood mononuclear cells from 4 to 60 days with peak titres 20 days post-infection (dpi). There was a transient viraemia from 4 to 14 dpi with a maximum titre of 1x10(4)genome copies/ml plasma. An antibody response to the transmembrane (TM) glycoprotein commenced 12 dpi but an antibody response to the capsid (CA) protein was detected in one animal only and not until 34 dpi. The results indicated that detection of BIV in infected Bali cattle would have a greater chance of success soon after infection and prior to the onset of a CA antibody response.

The non-toxic A subunit of Shiga toxin type 1 prevents replication of bovine immunodeficiency virus in infected cells

Shiga toxins are ribosome-inactivating proteins many of which are antiviral. Shiga toxin-producing Escherichia coli (STEC) may be pathogenic to humans, but are carried without ill effects by ruminants. We hypothesize that STEC have antiviral activity in ruminants, and showed previously that the non-toxic subunit A of Shiga toxin 1 (StxA1) acts selectively on cells infected with bovine leukemia virus, without harming normal cells, and that the numbers of intestinal STEC are inversely correlated with viral load in bovine leukemia virus-infected sheep. The purpose of the present study was to characterize StxA1 activity against a second bovine retrovirus, bovine immunodeficiency virus (BIV). Flow cytometry showed that StxA1 treatment induced apoptosis in BIV-infected cells but not in uninfected cells and immunoblot analysis showed that StxA1 curtailed synthesis of Gag p26 protein. A systematic electron microscopy description of BIV infection in fetal bovine lung fibroblasts showed an orderly sequence of changes in cell membrane, endoplasmic reticulum, Golgi, nucleus, and mitochondria, and suggested that the infected cells produce the virus within multivesicular bodies (MVBs). StxA1 interfered with all manifestations of BIV-induced transformation of infected cells into BIV-producing units. BIV-infected cells provided a suitable experimental system for investigation of the mechanism of Stx-antiviral activity.

In vivo transcription of bovine leukemia virus and bovine immunodeficiency-like virus

Cellular tropism and transcription of bovine leukemia virus (BLV) and bovine immunodeficiency-like virus (BIV) were investigated using peripheral blood mononuclear cells (PBMC) collected from a cow infected with both viruses. Each PBMC subset, purified by magnetic cell sorting, was subjected to PCR and RT-PCR for detection of their integrated proviruses and transcript mRNAs. Both BLV and BIV genomes were detected by nested PCR in CD3(+), CD4(+), CD8(+) and gammadelta T cells, B cells and monocytes. However, BLV tax transcription was only detected in B cells, and only B cells also formed BLV syncytia in CC81 cells. On the other hand, BIV transcript was detected in each subpopulation of PBMC. These results indicated that BLV can infect T cells and monocytes as well as B cells, but can be expressed by transcription only in B cells. In contrast, BIV can express its transcripts in all infected cells.

Natural bovine lentiviral type 1 infection in Holstein dairy cattle. I. Clinical, serological, and pathological observations

Clinical, serological, and pathological abnormalities observed in Holstein cows naturally infected with bovine lentivirus 1 bovine immunodeficiency virus (BIV) and other infections were progressive and most commonly associated with weight loss, lymphoid system deficiency, and behavioral changes. Clinical evidence of meningoencephalitis was dullness, stupor, and occasional head or nose pressing postures. The polymerase chain reactions associated the BIV provirus with the lesions in the central nervous system and lymphoid tissues. Multiple concurrent infections developed in retrovirally infected cows undergoing normal stresses associated with parturition and lactation. A major functional correlate of the lymphoreticular alterations was the development of multiple secondary infections which failed to resolve after appropriate antibacterial therapy. The chronic disease syndrome in dairy cows associated with BIV may be useful as a model system for investigation of the pathogenesis of the nervous system lesions and lymphoid organ changes that occur in humans with lentiviral infection.

Bovine immunodeficiency virus expression in vitro is reduced in the presence of beta-chemokines, MIP-1alpha, MIP-1beta and RANTES

The inhibition of HIV expression in vitro by a cocktail of the beta-chemokines MIP-1alpha, MIP-1beta and RANTES provided the initial evidence that HIV utilizes chemokine receptors as co-receptors for infection of cells. Bovine immunodeficiency virus (BIV), a lentivirus, infects a wide variety of leukocyte populations, but the cellular receptor(s) utilized by this virus for infection of cells is not known. The purpose of this study was to determine whether MIP-1alpha, MIP-1beta and RANTES affect BIV expression in vitro, as a prelude to identifying the cellular receptors utilized by this virus. Fetal bovine lung (FBL) cells were pretreated with serial dilutions of a cocktail of the chemokines, and then the cells were infected with BIV. Virus expression in these cells was determined by counting the syncytia that had developed in the cultures by five days after infection. A significant decrease in syncytium formation, corresponding to increasing concentrations of the chemokines, was the result. Reacting the chemokines with chemokine-specific neutralizing antibodies prior to treatment of the cells neutralized the effect of the chemokines on virus replication in a dose-dependent manner, restoring viral expression to a level similar to that of untreated cells. The presence of a CCR5 homologue on the surface of FBL cells was confirmed using an anti-CCR5 monoclonal antibody and FACS analysis. Collectively, these data provide preliminary evidence that BIV may utilize the CCR5 receptor for infection of cells in vitro, but additional studies are necessary to confirm this.

Experimental collection and transfer of embryos from bovine immunodeficiency virus (BIV) infected cattle

Three experiments were conducted to determine whether the lentivirus, bovine immunodeficiency virus (BIV) is likely to be transmitted via embryo transfer. In the first experiment, embryos collected from BIV-negative heifers were exposed in vitro to BIV for 24 h, washed and then tested for the presence of the provirus. In the second experiment, embryos obtained from BIV-negative heifers were transferred to the uterine horns of BIV-infected heifers; 24 h later these embryos were recovered and tested for the presence of BIV. In the third experiment, embryos were collected from heifers experimentally infected with BIV and then transferred to BIV-negative recipients. In all three experiments, (BIV) proviral DNA was not detected by PCR in association with any oocytes, embryos, follicular fluid, oviductal or uterine washes. Twelve single embryos collected from BIV experimentally infected donors were transferred to BIV-negative recipients resulting in the birth of 7 calves all of which were also negative for BIV; the recipients remained BIV-negative throughout the experiment. In conclusion, this study demonstrates that it is possible to produce transferrable stage embryos from donors infected with BIV and that such embryos are unlikely to transmit this agent either to the recipients or the resulting offspring.

Serological evidence of an Australian bovine lentivirus

Recombinant 26 kDa capsid (CA) proteins of bovine lentiviruses, bovine immunodeficiency virus (BIV) and Jembrana disease virus (JDV), were expressed in Escherichia coli and utilised as antigens for an enzyme-linked immunosorbent assay (ELISA) and a western immunoblot (WIB) procedure for the detection of antibody in dairy cattle in Western Australia. A total of 690 serum samples, 30 from each of 23 farms, were tested by ELISA with a JDV CA protein antigen, and antibody was detected in 3.8% (p<0.05) of the sera. Nine sera from each farm were also tested by WIB with JDV CA protein antigens and antibody was detected in 15.9% of these samples. All ELISA-positive results were also WIB-positive, and all sera antibody-positive by WIB with JDV CA protein antigens were also antibody-positive by the WIB using recombinant BIV CA antigens. This study showed that recombinant protein antigens can be used for serological tests to detect bovine lentivirus infection in Australia.

Natural selection of the Pol gene of bovine immunodeficiency virus

Genetic variability is a salient feature of lentiviruses, contributing to the pathogenesis of these viruses by enabling them to persist in the host and to resist anti-retroviral treatment. Bovine immunodeficiency virus (BIV), a lentivirus of unknown pathology, infects cattle in the United States and worldwide. Genetic diversity of BIV that is associated with naturally infected cattle is not well studied. We examined the genetic diversity and natural selection of a segment of the BIV pol gene amplified from the leukocyte DNA of naturally infected cattle. A portion of the reverse transcriptase domain (183 bp) of the pol region was targeted for amplification by PCR. PCR products were sequenced directly and aligned. When compared to the sequences of BIV R29-127, a molecular clone of the original BIV R29 isolate, all isolates were greater than 91% identical in nucleotide sequences and 77% identical in amino acid sequences. Pol genotypes were polymorphic at 14% of the nucleotide sites. The ratio of nonsynonymous to synonymous nucleotide substitutions (relative to the number of respective sites, Ka/Ks) was 0.16, indicating that this region of the BIV genome, like that of HIV-1, is subject to purifying selection. Based on the McDonald-Kreitman analysis, this region also was under positive Darwinian selection as HIV-1 and BIV diverged from a common progenitor. Phylogenetic analysis revealed that genotypes were geographically distinct, possibly indicating a common source of infection for animals within a herd.

Seroprevalence and field isolation of bovine immunodeficiency virus

A seroprevalence study of bovine lentivirus, known as bovine immunodeficiency virus (BIV), was conducted in 12 different dairy herds in Hokkaido, where some herds were a high prevalence of bovine leukemia virus (BLV) infection. Amongst 611 cattle, 28.6% of cattle were BLV-seropositive, and 11.7% of cattle were seropositive for BIV, while 4.2% of cattle were seropositive for both BIV and BLV. For the isolation of BIV, 19 samples of peripheral blood mononuclear cells (PBMC) and one sample of milk-derived leukocytes were prepared from BIV-seropositive cows. These PBMC and leukocyte preparations were then co-cultivated with cc81 cells, a cat cell line transformed by mouse sarcoma virus. BIV was isolated from 17 PBMC and one milk-derived leukocyte samples. The isolated viruses showed slow replication and syncytia formation. Major core antigen, p26 from these isolates were reacted with anti-BIV (American isolate R-29) serum. In addition, proviral DNA was detected in blood and milk samples by nested polymerase chain reaction and subsequent Southern blot hybridization. Nucleotide sequence analysis of the amplified pol gene products showed its 99.0 to 99.7% homology to that of BIV R-29. These results indicate that the Japanese BIV isolates appear to be antigenically and genetically similar to the American R-29. Since BIV was isolated from milk samples, BIV could possibly be transmitted through milk. This is the first report of BIV isolation in Japan.

Investigation of the cellular tropism of bovine immunodeficiency-like virus

Bovine immunodeficiency-like virus (BIV) was first isolated from an animal showing transient leucocytosis, lymphadenopathy, lesions in the central nervous system and progressive weakness and emaciation. Similar signs are observed in other immunosuppressive lentiviral infections. BIV, like other lentiviruses, has been isolated from peripheral blood mononuclear cells and lymphoid tissue of infected animals. However, the in vivo cellular tropism of BIV remains unclear although initial studies indicate that BIV may be pantropic, infecting T cells, B cells and monocytes similar to some of the immunodeficiency-causing lentiviruses. PCR, Southern blot hybridisation, cell culture and reverse transcriptase assays were used to demonstrate the presence of BIV proviral DNA and the production of infectious virus in CD2+, WC1+, B cells and monocytes during the acute stages of infection. Western immunoblot assays were used to assess the development of antibody responses towards the virus.